The human placental epithelium performs a critical function in maintaining normal fetal development by mediating the transfer or organic and inorganic metabolites between the fetal and maternal circulations. Presently, little is known about anion transport mechanisms specific to the basal and microvillus membrane domain of human placental epithelial cells and nothing is known about their molecular structure. Accordingly, the objective of the proposed research is to identify and characterize ion-coupled anion transport pathways located in the basal (fetal-facing) and microvillus (maternal-facing) membranes of human placental epithelial cells. Purified basal and microvillus membrane vesicle preparations will be used to study ion-coupled anion transport mechanisms present at the fetal and maternal side of placental epithelial cells. The functional identity and properties of organic and inorganic anion cotransport mechanisms present in basal and microvillus membrane vesicles will be assessed from radiolabelled tracer flux assays and fluorescence measurements. Candidates for cotransport include chloride, iodide, fluoride, sulfate, bicarbonate, mono- and dicarboxylate metabolites, acidic amino acids and the vitamins biotin, pantothenate, folate, nicotinate and ascorbate. Functional assays of anion transport activity in membrane vesicles will serve as a means to evaluate the affinity and specificity of chemical probes to be used for the biochemical identification of membrane proteins as structural correlates or organic and inorganic transport function. Radiolabeled photoaffinity probes will be synthesized to label organic and inorganic anion transport proteins in microvillus and basal membranes. Labeled membrane proteins will be identified by gel-electrophoresis and autoradiography. Future studies include: isolation and purification of functional anion transport proteins using affinity chromatography and reconstitution of transport activity in artificial liposomes, develop monoclonal antibodies to the identified anion transport proteins and purification of human placental mRNA for expression of functional anion transport proteins in mRNA injected frog oocytes. Information obtained from the proposed studies should contribute new ideas toward explaining the placental pathophysiology involved in intrauterine growth retardation.